Add a readme to explain a bit how run tests

tests/README.md

+# Tests with Catch
+The tests are written by utilizing the Catch framework, a header-only test
+framework. The main test file includes all test header files to be able to use
+the command line tool that is added with the ```#define CATCH_CONFIG_MAIN```.
+See the Catch framework on github for more information about this.
+
+## How to run
+Until a script is added to run these test aumatically upon make, the tests can
+be executed by:
+
+~~~Shell
+$ <eos_root_install_dir>/tests/main-tests
+~~~
+
+Note that we execute all tests with this command. For help, pass ``-h``` to the
+main-test binary file.
+
+~~~Shell
+$ <eos_root_install_dir>/tests/main-tests -h
+~~~
+
+For example if the root install dir is right in this folder (as the main README
+suggests with ```-DCMAKE_INSTALL_PREFIX```), then do:
+
+~~~Shell
+$ ./install/tests/main-tests'
+~~~
+
+If you are using the docker files from the docker branch, the command looks
+like this:
+
+~~~Shell
+$ CMD='cd build/tests; make -j4 && make install && cd ../../ && ./install/tests/main-tests' make run-bash-cmd
+~~~
+
+## References
+* Catch on github [Catch framework](https://github.com/philsquared/Catch)